Converter one pin sensing

ABSTRACT

Power converters, such as switched-mode power converters comprise a reduced number of sensing pins. A power converter is configured to convert electrical energy at an input voltage into electrical energy at an output voltage. The power converter comprises a power switch configured to be switched between on- and off-states; and a controller configured to generate a control signal for putting the power switch into the on-state and off-state, respectively; wherein the control signal is generated based on a first and second measurement signal from the power converter external to the controller. The controller comprises a sensing pin configured to sense the first measurement signal, when the power switch is in on-state, and configured to sense the second measurement signal, when the power switch is in off-state.

TECHNICAL FIELD

The present document relates to power converters, such as switched-modepower converters. In particular, the present document relates to powerconverters comprising a reduced number of sensing pins.

BACKGROUND

Switched-mode power converters typically comprise a power converternetwork comprising one or more power switches and a controllerconfigured to control the one or more power switches. In particular, thecontroller may be configured to control the time instances at which theone or more power switches are put into an on-state and into anoff-state. The controller may comprise one or more sensing pinsconfigured to receive various measurement signals from the powerconverter network. The controller may use the measurement signals tocontrol the one or more power switches. In typical implementations ofpower converters, several different sensing pins are used for severaldifferent measurement signals. By way of example, a typical approach isto use several different pins for current sensing and voltagemeasurements, respectively.

Power converters, e.g. power converters which are used in retrofit lampdriver circuits, are strongly constrained in cost, size and componentcount. As a consequence, integrated circuits (ICs) used in such powerconverters (e.g. as controllers) should be designed with a minimumnumber of pins. Minimizing the pin count typically reduces the number ofexternal components, the losses in sensor elements (voltage dividers,shunts) and the chip area required for additional pads and analogsensing blocks. Hence, the pin count is an important cost driver for lowcost power converters.

In the present document, power converters are described which allow thesensing of multiple measurement signals using a single sensing pin. Byway of example, a flyback power converter with one pin sensing (forsystem detection, current measurement, bus voltage measurement and/oravalanche measurement) is described. Furthermore, a power factorcorrection (PFC) with a multi-function pin for simultaneous detection ofthe input voltage, the bus voltage and/or for zero-crossing timingmeasurement is described.

SUMMARY

According to an aspect of the invention, a power converter configured toconvert electrical energy at an input voltage into electrical energy atan output voltage is described. The power converter may comprise aswitched-mode power converter, such as a SEPIC, a flyback converter, abuck converter, a boost converter, and/or a buck-boost converter. Theinput voltage may correspond to the voltage at an input of the powerconverter (e.g. upstream of a power switch of the power converter) andthe output voltage may correspond to the voltage at an output of thepower converter (e.g. downstream of the power switch of the powerconverter). The power converter may comprise one or more converterstages, wherein each converter stage may comprise a switched-mode powerconverter.

The power converter may comprise a power switch configured to beswitched between an on-state and an off-state. The power switch maycomprise or may be implemented as a transistor, e.g. a metal-oxidesemiconductor field effect transistor. The power switch may becontrolled using a control signal generated by a controller. The controlsignal may comprise a pulse width modulated signal, thereby putting thepower switch in the on-state and the off-state in a commutated manner.

The power converter may comprise the controller configured to generatethe control signal for putting the power switch into the on-state andinto the off-state, respectively. Typically, the control signal isapplied to a gate of the power switch. The controller may be configuredto generate the control signal based on a first measurement signaland/or based on a second measurement signal. The first and/or secondmeasurement signals may be measurement signals from the power converter.In particular, a measurement signal may be determined at a node withinthe power converter, wherein the node is external to the controller. Themeasurement signal may be indicative of a voltage or a current at thecorresponding node within the power converter. Examples for the firstmeasurement signal are e.g. the input voltage of the power converterand/or a current through the power switch. Examples for the secondmeasurement signal are the input voltage of the power converter and/orthe voltage drop at a transformer or a winding/coil of the powerconverter. The first and second measurement signals are typicallydifferent from one another. In particular, the first and secondmeasurement signals are typically determined at different nodes withinthe power converter.

The controller, which may be implemented e.g. as an integrated circuitcomprising a plurality of pins, may comprise one or more sensing pins.In particular, the controller may comprise a sensing pin configured tosense the first measurement signal, when the power switch is inon-state, and configured to sense the second measurement signal, whenthe power switch is in off-state. As such, the controller may beprovided with a plurality of different measurement signals using only asingle sensing pin, thereby reducing the cost of the power converter.

The power converter may comprise a voltage divider coupled to the inputvoltage of the power converter. By way of example, the input voltage ofthe power converter may correspond to (a rectified version of) the mainsvoltage. The voltage divider may comprise a high side resistor coupledto the input voltage and/or a low side resistor coupled to ground (orsome other pre-determined potential). The high side resistor and/or amidpoint between the high side resistor and the low side resistor may becoupled to the sensing pin, thereby providing the first measurementsignal. In this case, the first measurement signal may be indicative ofthe input voltage. The low side resistor may be implemented within thecontroller.

Alternatively, the voltage divider may be formed using a current mirrorwhich is internal to the controller. In particular, the voltage dividermay comprise a current mirror arranged in series with a second currentsource. The current mirror and the second current source may be internalto the controller. A first side of the current mirror may be coupled tothe sensing pin and a second side of the current mirror may be coupledto the second current source. The controller may comprise a secondcomparator configured to measure the first measurement signal at thesecond side of the current mirror. The controller may comprise anadditional switch arranged between the sensing pin and the first side ofthe current mirror and configured to decouple the current mirror fromthe sensing pin, when sensing the second measurement signal. The use ofa current mirror may be beneficial in order to lower the level of thefirst measurement signal. This may be achieved e.g. by using a currentmirror comprising MOS transistors with a MOS diode.

As such, the first measurement signal may be used by the controller todetermine one or more events which are encoded into the input voltage.By way of example, the controller may be configured to operate the powerconverter according to a current operation state. Furthermore, thecontroller may be configured to detect one of a plurality ofpre-determined events based on the first measurement signal (e.g. basedon the indication of the input voltage). In addition, the controller maybe configured to determine a target operation state in accordance with apre-determined state machine, based on the current operation state andbased on the detected one of the plurality of pre-determined events. Thepower converter may then be operated in accordance with the targetoperation state. By way of example, the power converter may be used in adriver circuit for a light bulb assembly. As such, the operation statesof the power converter may correspond to different illumination statesof the light bulb assembly:

The power converter may comprise a transformer comprising a primarywinding and an auxiliary winding. The primary winding and the auxiliarywinding may be electromagnetically coupled. An example of a powerconverter which comprises a transformer is a power converter having aSEPIC architecture. The primary winding of the transformer may bearranged in series with the power switch. In particular, the primarywinding may be arranged such that the primary winding may be coupled toground via the power switch, when the power switch is in on-state. Theauxiliary winding may be coupled to the sensing pin, thereby providingthe second measurement signal. In such a case, the second measurementsignal may be indicative of the voltage drop across the transformer,i.e. the voltage drop across the auxiliary winding which typicallycorresponds to the voltage drop across the primary winding. The voltagedrop across the transformer may be used to detect free-wheeling of thetransformer (i.e. to detect the time instant, when the current throughthe primary winding drops to substantially zero).

As such, a single sensing pin of the controller may be used to providethe controller with information regarding the input voltage (e.g. forcontrolling the operational state of the power converter) and withinformation regarding free-wheeling of the transformer of the powerconverter (e.g. for determining the time instant for putting the powerswitch to on-state).

The auxiliary winding may be coupled to the sensing pin via a diode. Thediode may be reverse biased, when the power switch is in on-state,thereby decoupling the auxiliary winding from the sensing pin, when thepower switch is in on-state. By doing this, it is ensured that theprovision of the first measurement signal is not disturbed by the secondmeasurement signal (provided via the auxiliary winding).

The controller may comprise a current source which is coupled to thesensing pin of the controller via a control switch. The current sourcemay be coupled to ground (or to another pre-determined potential). Thecontroller may be configured to open the control switch, when the powerswitch is put to on-state. Furthermore, the controller may be configuredto close the control switch, when the power switch is put to off-state.The control switch and the current source may be arranged in parallel tothe low side resistor of the voltage divider. Furthermore, the controlswitch and the current source may exhibit low impedance compared to thelow side resistor. As such, it is ensured that the provision of thesecond measurement signal to the controller is not disturbed by thefirst measurement signal (provided by the voltage divider).

The controller may comprise a comparator (which may be based on anoperational amplifier) configured to measure a voltage at the sensingpin. In particular, the comparator may be configured to compare thevoltage at the sensing pin to a reference voltage, thereby indicatingwhether the voltage at the sensing pin is greater or smaller than thereference voltage. As such, the controller may be configured todetermine whether the first measurement signal is greater or smallerthan a reference voltage (when the power switch is in on-state) andwhether the second measurement signal is greater or smaller than a(possibly different) reference voltage (when the power switch is inoff-state).

As indicated above, the power converter may comprise a transformer. Thetransformer may comprise a primary winding and a secondary winding. Thismay be the case, e.g. for a flyback power converter. The power convertermay comprise a voltage divider coupled to the input voltage via theprimary winding of the transformer. The voltage divider is typicallydifferent from the voltage divider described above. In particular, thevoltage divider may be arranged in parallel to the power switch. Thevoltage divider may comprise a high side resistor coupled to the inputvoltage via the primary winding of the transformer and a low sideresistor coupled to ground (or another pre-determined potential). Thelow side resistor may be coupled to ground (or to another pre-determinedpotential) via a shunt resistor. A midpoint between the high sideresistor and the low side resistor may be coupled to the sensing pin,thereby providing the second measurement signal. The second measurementsignal may be indicative of the input voltage. Furthermore, the secondmeasurement signal may be indicative of a voltage drop across theprimary winding of the transformer.

As such, a discontinuity of the second measurement signal may beindicative of a free-wheeling of the primary winding of the transformer,thereby indicating the time instant when the current through the primarywinding of the transformer reaches substantially zero.

The power converter may comprise a shunt resistor, wherein the shuntresistor may be arranged in series with the voltage divider and inseries with the power switch. The shunt resistor may be coupled to themidpoint of the voltage divider via the low side resistor, therebyproviding the first measurement signal to the sensing pin of thecontroller. As such, the controller may be provided with informationregarding the current through the power switch.

Overall, the controller may be provided with a second measurementsignal, which is indicative of the input voltage and the free-wheelingof the primary winding of the transformer, and with a first measurementsignal, which is indicative of the current through the power switch,using only a single sensing pin, thereby reducing the cost of the powerconverter.

The power converter may comprise a supply voltage capacitor coupled to asupply voltage pin of the controller. The controller may be configuredto couple the sensing pin to the supply voltage pin, upon startup of thepower converter to charge the supply voltage capacitor via the high sideresistor of the voltage divider. In particular, the controller maycomprise a startup diode which is configured to let pass a current fromthe sensing pin to the supply voltage pin, and which is configured toblock a current from the supply voltage pin to the sensing pin and/or tomeasurement circuitry used to measure the first and/or secondmeasurement signals. As such, the startup diode may be configured toallow for a charging of the supply voltage capacitor using the high sideresistor of the voltage divider. On the other hand, the startup diodemay be configured to decouple the supply voltage capacitor (i.e. thesupply voltage pin) from the measurement circuitry used to measure thefirst and/or second measurement signals.

It should be noted that the low side resistor of the voltage divider maybe internal to the controller. The low side resistor may be part of themeasurement circuitry. As such, the power converter may comprise a highside resistor which is external to the controller and which may be usedto provide a startup current to the supply voltage capacitor.Furthermore, the power converter may comprise a low side resistor whichis internal to the controller and which forms a voltage divider with theexternal high side resistor, when the startup switch is closed.

The controller may further comprise a startup switch configured todecouple the measurement circuitry for measuring the first and secondmeasurement signals, when the startup switch is open. On the other hand,the startup switch may be configured to couple the sensing pin with themeasurement circuitry, when the startup switch is closed. The startupswitch may be arranged in series with the supply voltage pin and thestartup diode on one side of the startup switch and with the measurementcircuitry on the other side of the switch. As such, the startup switchmay be used to avoid an impact of the measurement circuitry on thecharging of the supply voltage capacitor. The measurement circuitry maycomprise the current source, the control switch and/or the comparatorused to determine the first and/or second measurement signals.

According to a further aspect, a driver circuit, e.g. a driver circuitfor a light source such as a solid state light (SSL) source, isdescribed. The driver circuit may comprise the power converter describedin the present document.

According to another aspect, a light bulb assembly is described. Thelight bulb assembly comprises an electrical connection module configuredto electrically connect to a mains power supply, thereby providingelectrical energy at the input voltage. Furthermore, the light bulbassembly comprises a power converter as described in the presentdocument. The power converter may be configured to provide electricalenergy at an output voltage from the electrical energy at the inputvoltage. In addition, the light bulb assembly comprises a light source(e.g. an SSL source such as an LED array or an OLED array) configured toprovide light using the electrical energy at the output voltage.

According to another aspect, a method for converting electrical energyat an input voltage into electrical energy at an output voltage isdescribed. The method comprises switching a power switch of a powerconverter between an on-state and an off-state, subject to a controlsignal. Furthermore, the method comprises providing a first measurementsignal from the power converter to a controller via a sensing pin of thecontroller, when the power switch is in on-state. The first measurementsignal may be provided using a voltage divider coupled to the inputvoltage. In addition, the method comprises providing a secondmeasurement signal from the power converter to the controller via thesame sensing pin of the controller, when the power switch is inoff-state. The second measurement signal may be provided using atransformer comprising a primary winding arranged in series with thepower switch. The control signal for putting the power switch into theon-state and into the off-state, respectively, may be generated by thecontroller based on the first and/or the second measurement signal.

According to a further aspect, a software program is described. Thesoftware program may be adapted for execution on a processor and forperforming the method steps outlined in the present document whencarried out on the processor.

According to another aspect, a storage medium is described. The storagemedium may comprise a software program adapted for execution on aprocessor and for performing the method steps outlined in the presentdocument when carried out on the processor.

According to a further aspect, a computer program product is described.The computer program may comprise executable instructions for performingthe method steps outlined in the present document when executed on acomputer.

It should be noted that the methods and systems including its preferredembodiments as outlined in the present document may be used stand-aloneor in combination with the other methods and systems disclosed in thisdocument. In addition, the features outlined in the context of a systemare also applicable to a corresponding method. Furthermore, all aspectsof the methods and systems outlined in the present document may bearbitrarily combined. In particular, the features of the claims may becombined with one another in an arbitrary manner.

In the present document, the term “couple” or “coupled” refers toelements being in electrical communication with each other, whetherdirectly connected e.g., via wires, or in some other manner.

SHORT DESCRIPTION OF THE FIGURES

The invention is explained below in an exemplary manner with referenceto the accompanying drawings, wherein

FIG. 1 illustrates a block diagram of an example light bulb assembly;

FIG. 2 a shows a circuit diagram of an example switched-mode powerconverter;

FIG. 2 b shows an excerpt of an example power converter using a singlesensing pin for measuring the input voltage and for measuringfree-wheeling;

FIG. 2 c shows an excerpt of another example power converter using asingle sensing pin for charging the supply voltage capacitor, formeasuring the input voltage and for measuring free-wheeling;

FIG. 2 d shows an excerpt of a further example power converter using asingle sensing pin for charging the supply voltage capacitor, formeasuring the input voltage and for measuring free-wheeling (wherein thecircuit for measuring free-wheeling is not shown);

FIG. 3 illustrates an example method for controlling the illuminationlevel of a light bulb assembly based on events detected from the mainsvoltage; and

FIG. 4 shows a flow chart of an example method for providing a pluralityof measurement signals using a single sensing pin.

DETAILED DESCRIPTION

In the present document, a light bulb “assembly” includes all of thecomponents required to replace a traditional incandescent filament-basedlight bulb, notably light bulbs for connection to the standardelectricity supply. In British English (and in the present document),this electricity supply is referred to as “mains” electricity, whilst inUS English, this supply is typically referred to as power line. Otherterms include AC power, line power, domestic power and grid power. It isto be understood that these terms are readily interchangeable, and carrythe same meaning.

Typically, in Europe electricity is supplied at 230-240 VAC, at 50 Hz(mains frequency) and in North America at 110-120 VAC at 60 Hz (mainsfrequency). The principles set out in the present document apply to anysuitable electricity supply, including the mains/power line mentioned,and a DC power supply, and a rectified AC power supply.

FIG. 1 is a schematic view of a light bulb assembly. The assembly 1comprises a bulb housing 2 and an electrical connection module 4. Theelectrical connection module 4 can be of a screw type or of a bayonettype, or of any other suitable connection to a light bulb socket.Typical examples of an electrical connection module 4 are the E11, E14and E27 screw types of Europe and the E12, E17 and E26 screw types ofNorth America. Furthermore, a light source 6 (also referred to as anilluminant) is provided within the housing 2. Examples of such lightsources 6 are a CFL tube or a solid state light source 6, such as alight emitting diode (LED) or an organic light emitting diode (OLED)(the latter technology is referred to as solid state lighting, SSL). Thelight source 6 may be provided by a single light emitting diode, or by aplurality of LEDs:

Driver circuit 8 is located within the bulb housing 2, and serves toconvert supply electricity received through the electrical connectionmodule 4 into a controlled drive current for the light source 6. In thecase of a solid state light source 6, the driver circuit 8 is configuredto provide a controlled direct drive current to the light source 6.

The housing 2 provides a suitably robust enclosure for the light sourceand drive components, and includes optical elements that may be requiredfor providing the desired output light from the assembly. The housing 2may also provide a heat-sink capability, since management of thetemperature of the light source may be important in maximising lightoutput and light source life. Accordingly, the housing is typicallydesigned to enable heat generated by the light source to be conductedaway from the light source, and out of the assembly as a whole.

The driver circuit 8 of a light bulb assembly 1 should be configured toprovide a drive current to the light source 6 almost instantaneously,subsequent to turning on of the mains supply (e.g. subsequent to a userswitching on the light). Consequently, the driver circuit 8 shouldexhibit a low start-up time. On the other hand, the driver circuit 8should be configured to measure the mains supply which may be used toencode events which may be used to control the behaviour of the lightbulb assembly 1. By way of example, intentional interruptions of themains supply may enable a user to control the dimming of the light bulbassembly 1 using an on/off light switch. The driver circuit 8 should beconfigured to determine such interruptions.

FIG. 2 a illustrates an example circuit diagram of a driver circuit 8,100 for an LED (light emitting diode) array 6, 120. The driver circuit100 may be used in a retrofit light bulb assembly 1 as described inFIG. 1. The driver circuit 100 comprises a rectifier 102 in combinationwith EMI (electromagnetic interference) filter components 103, 104,which are configured to provide a DC input voltage from a mains supply101. Furthermore, the driver circuit 100 comprises a controller 160which may be implemented as an integrated circuit (IC). The supplyvoltage for the controller 160 may be maintained using a supply voltagecapacitor 111. The controller 160 comprises a startup and input voltagesensing pin 130, which is coupled to the (non-rectified) input voltageusing the startup resistors 161. The particular arrangement of thestartup resistors 161 ensures that the voltage at the startup and inputvoltage sensing pin 130 is always positive. This is illustrated in FIG.2 c, where it can be seen that the startup resistors 161 are arranged incombination with the full-wave rectifier 102, such that the voltage atthe startup and input voltage sensing pin 130 is always positive.

Furthermore, FIG. 2 c shows that the startup resistors 161 may becoupled to the supply voltage capacitor 111 via a diode function 221which may be internal to the controller 160. For startup, the switch 222may be opened, thereby coupling the input voltage via the startupresistors 161 to the supply voltage capacitor 111. When closing theswitch 222, the voltage drop will be significantly lower than the supplyvoltage Vcc, such that the diode function 222 is reverse-biased, therebydecoupling the supply voltage capacitor 111 from the pin 130.

The driver circuit 100 of FIG. 2 a comprises a dual-stage powerconverter. The controller 160 provides at least two output pins 151, 152for providing respective pulse width modulated control signals to thetwo power switches 163, 173 (which may be implemented as transistors,e.g. as metal oxide semiconductor field effect transistors, MOSFETs) ofthe two converter stages. The driver circuit 100 of FIG. 2 a makes useof a dual stage SEPIC/Flyback converter, wherein the first converter (aSEPIC converter) 191 comprises the components 162, 163, 164, 165, 166and wherein the second converter (a flyback converter) 192 comprises thecomponents 172, 173, 175, 176. In the illustrated example, the secondconverter stage provides for the SELV (Separated or safety extra-lowvoltage) requirements.

As indicated above, the controller 160 comprises the startup and inputvoltage sensing pin 130 which is configured to provide an initial chargeto the supply voltage capacitor 111 upon startup of the driver circuit100, thereby allowing the controller 160 to start operation.Furthermore, the startup and input voltage sensing pint 130 may be usedto sense the input voltage provided by the mains supply 101. This may beused to sense events encoded in the input voltage (e.g. encoded in themains supply), as will be described in the context of FIG. 3. Thecontroller 160 may be configured to control an illumination state of theLED array 120 based on a detected event (e.g. as described in thecontext of FIG. 3).

As indicated above, the first converter stage of the driver circuit 100comprises a SEPIC (Single-ended primary-inductor converter) comprising aSEPIC transformer 162. The transformer 162 comprises a primary winding181 and a secondary winding 182 which form the SEPIC converterstructure. Furthermore, the transformer 162 may comprise an auxiliarywinding 183 which may be used for measurement purposes. In particular,the auxiliary winding 183 may be used to detect the zero crossing of theinductor current through the primary winding 181, when the power switch163 of the SEPIC is in off-state. The zero crossing of the inductorcurrent typically corresponds to the time instant when no more energy isstored in the primary winding 181, and is often referred to asfree-wheeling. The detection of the zero crossing of the inductorcurrent (i.e. the detection of free-wheeling) is beneficial, as itallows the power switch 163 to be switched to the on-state, at a timeinstant when the inductor current is substantially zero. As a result,the power losses of the SEPIC can be reduced and the lifetime of thepower switch 163 can be increased.

In the present document, it is proposed to use the startup and inputvoltage sensing pin 130 also to enable the controller 160 to measure thezero crossing of the inductor current of the SEPIC. For this purpose,the auxiliary winding 183 of the SEPIC transformer 162 is coupled to thepin 130 via a diode 131 and a resistor 132, thereby overlaying the inputvoltage measurement signal (provided via the startup resistors 161) andthe inductor current measurement signal (provided via the auxiliarywinding 183 of the SEPIC transformer 162). The diode 131 may be used todecouple the auxiliary winding 183 from the startup resistors 161 attime instants when the power switch 163 is closed (and energy is storedin the transformer 162). The resistor 132 may be used to prevent currentpeaks. The controller 160 may be configured to separate the overlaidmeasurement signals received via pin 130. The separation of the overlaidmeasurement signals may be performed using digital signal processingtechniques. Alternatively or in addition, the separation of the overlaidmeasurements signals may be performed using appropriate circuitry and/ortemporal separation. By way of example, a first measurement signal maybe measured during a first time period (e.g. when the power switch 163is closed) and a second measurement signal may be measured during asubsequent second time period (e.g. when the power switch 163 is open).

FIG. 2 b shows an excerpt diagram 200 of the driver circuit 100 of FIG.2 a. In particular, FIG. 2 b illustrates how the measurement of theinput voltage and the measurement of the inductor current (i.e. themeasurement of free-wheeling) may be performed using a single pin 130 ofthe controller 160. The circuit diagram 200 of FIG. 2 b shows a voltagedivider comprising the resistors 201, 202. The voltage divider 201, 202may be used to sense the input voltage (derived e.g. from the mainssupply) of the driver circuit 100. Furthermore, the circuit diagram 200shows the diode D2 131 and the resistor R4 132 which are coupled to theauxiliary winding 183 of the transformer 162.

The controller 160 may comprise a control switch S1 203 and a currentsource 204. The current source 204 may be switched in synchronizationwith, e.g. in accordance to, the power switch 163. If the power switch163 is put into off-state (or high impedance state), the current source204 may be switched on (e.g. by closing the control switch S1 203). Onthe other hand, if the power switch 163 is put into on-state, thecurrent source 204 may be switched off (e.g. by opening the controlswitch S1 203). The free-wheeling detection or the measurement of thevoltage subsequent to the diode D2 131 may be performed when the currentsource 204 is on. As such, the current source 204 provides a lowimpedance path with respect to the voltage divider 201, 202, and theauxiliary winding 183, the resistor R4 132 and the diode D2 131 arecoupled with low impedance to the controller IC 160. The low impedancecoupling of the auxiliary winding 183 to the controller 160 isbeneficial, in order to rapidly discharge parasitic capacitors, whendetecting free-wheeling (i.e. when detecting the zero crossing of theinductor current). The measurement signal for free-wheeling typicallycomprises high frequency components and should therefore be coupled tothe controller 160 via a relatively low impedance.

In other words, the measurement of the input voltage via the voltagedivider 201, 202 may be performed during a first time period, when thepower switch 163 is in on-state and when the control switch S1 203 isopen. The auxiliary winding 183 of the transformer 162 may be polarizedsuch that the voltage drop at the auxiliary winding 183 is negative(with respect to ground), when there is a current ramping up in theprimary winding 181 of the transformer 162. As a result, the diode D2131 decouples the auxiliary winding 183 from pin 130 of the controller160, thereby enabling the measurement of the input voltage via thevoltage divider 201, 202 using the comparator 205 of the controller 160.

On the other hand, during a second time period, the power switch 163 maybe in off-state and the control switch S1 203 may be closed. The currentsource 204 may be implemented with a low impedance compared to the lowside resistor R2 202 of the voltage divider 201, 202, thereby forming aquasi short circuit of the low side resistor R2 202, i.e. therebydecoupling the measurement of the input voltage from the pin 130. On theother hand, the voltage drop across the auxiliary winding 183 can bemeasured using the comparator 205. In particular, a discontinuity of thevoltage drop across the auxiliary winding 183 (occurring at the timeinstant of the zero-crossing of the inductor current) can be detected,thereby detecting free-wheeling at the controller 160 (i.e. at thecomparator 205).

As indicated above, digital signal processing may be used to decode acomplex measurement signal comprising a linear superposition of multipletime dependent measurement signals. As such, a plurality of measurementsignals may be superimposed at an input pin 130 of the controller andthe superimposed measurement signals may be separated using digitalsignal processing and/or using temporal de-multiplexing. As such, a setof independent sensors and a set of different sensing pins may bereplaced by a reduced number of sensing pins. Due to the digital natureof the control algorithm, correction factors and error compensation maybe applied.

As outlined in the context of FIGS. 2 a and 2 b, the driver circuit 100may comprise a plurality of converter stages, e.g. a boost converterfollowed by a flyback converter. The free-wheeling detection of theSEPIC may be performed together with the voltage measurement of theinput voltage (e.g. of the mains voltage) using a single sensing pin130. The example SEPIC of FIGS. 2 a and 2 b comprises an optional diode131 for avoiding negative voltages and/or for decoupling. Alternatively,by changing the polarity and by providing an internal offset, negativevoltages can be detected. As such, the diode 131 may not be required.

For the flyback converter, the input voltage Vin of the flybackconverter, including free-wheeling, may be measured together with thecurrent through the flyback converter power switch 173 at the shuntresistor 141. If the power switch 173 is switched off, the input voltageVin to the flyback converter can be measured at the pin 140 via theresistor divider formed by the resistors 143, 142. The shunt resistor141 may have a relatively low resistance and may therefore not have asignificant influence for the measurement of the input voltage.Free-wheeling may be detected, by detecting a fast change of the voltagesensed at the pin 140. In other words, when the power switch 173 of theflyback converter is in off-state, the measurement signal at the pin 140is an indication of the bus voltage across the transformer 172, and thevoltage divider 143, 142. As long as there is a current flowing throughthe transformer 172, there is a voltage drop across the primary windingof the transformer 172. However, upon zero crossing of the current, thevoltage drops to zero, thereby causing a discontinuity of the voltage atthe pin 140. This discontinuity can be detected within the controller160, thereby detecting free-wheeling.

If the flyback converter power switch 173 is switched on, the voltageacross the drain/source of the switch 173 is typically low (in the rangeof 10 to 100 mV). This cancels out the voltage drop across the voltagedivider 143, 142 and by consequence the voltage at the shunt resistor141 can be measured, thereby providing an indication of the currentthrough the power switch 173. In other words, when the power switch 173is in on-state, the voltage divider 143, 142 is short circuited by thepower switch 173. As a result of this, the signal at pin 140 isindicative of the voltage drop at the shunt resistor 141, i.e. of thecurrent through the power switch 173.

As such, FIGS. 2 a and 2 b have provided examples of power converterscomprising a controller. The controller comprises at least one sensingpin which may be configured to measure a plurality of measurementsignals. In particular, the at least one sensing pin may be configuredto measure a first measurement signal, when the power switch of thepower converter is in on-state, and to measure a different secondmeasurement signal, when the power switch of the power converter is inoff-state. As such, the number of sensing pins of the controller may bereduced, thereby reducing the cost of the power converter.

As indicated above, the measurement of the input voltage to the drivercircuit 100 may be used to enable the driver circuit 100 to control theillumination state of the LED array 120, subject to one or more eventsdetected at the controller 160 based on the input voltage to the drivercircuit 100. As such, the driver circuit 100 of FIG. 2 a may beconfigured to control the illumination state of the LED array 120 basedon the input voltage sensed using the sensing pin 130.

FIG. 2 c shows an excerpt of another example power converter using asingle sensing pin for charging the supply voltage capacitor 111, formeasuring the input voltage of the power converter and for measuringfree-wheeling of the power converter. The sensing pin 130 is coupled tothe startup resistors 161 (resistors R1 and R2). Furthermore, thesensing pin 130 is coupled to the auxiliary winding 183 of thetransformer 162 of the boost converter. When the startup switch 222 isopen, the supply voltage capacitor 111 may be charged via the diode 221and the startup resistors 161. When closing the startup switch 222(which is typically internal to the controller 160), the diode 221decouples the supply voltage capacitor 111 from the sensing pin 130,thereby ensuring that the supply voltage capacitor 111 does not disturbthe measurement signals provided by the startup resistors 161 and by theauxiliary winding 183. As such, the startup switch 222 may be closed formeasuring the input voltage and/or for measuring free-wheeling.

The control switch 203 (referred to as S2 in FIG. 2 c) may be opened tomeasure the input voltage (e.g. the mains voltage at 230V) using thevoltage divider formed by the high side resistors 161 and the low sideresistor R3 223. On the other hand, the control switch 203 may be closedto measure the free-wheeling of the boost converter. In the latter case,the current I1 provided by the current source 204 will typically bedominant (compared to the current (i.e. the measurement signal) providedby the voltage divider formed by the resistors 161 and the resistor R3223). The voltage at the diode D7 131 and at the auxiliary winding 183may be measured when the signal is positive. A negative signal may notbe detectable by the circuit arrangement shown in FIG. 2 c.

FIG. 2 c shows an example, where the voltage divider for measuring theinput voltage is implemented using an internal resistor R3 223. Theinternal resistor 223 is preferably calibrated to a particular value, asIC technologies typically do not provide absolutely accurate resistors.As such, the voltage divider used to measure the input voltage isimplemented using the external resistors R1, R2 161 (forming the highside resistor) and the internal resistor R3 (forming the low sideresistor). The control switch 203 is kept open, when measuring the inputvoltage (via the voltage divider 161, 223). On the other hand, thecontrol switch 203 is closed, when measuring free-wheeling.

It should be noted that the internal resistor R3 223 may be decoupledusing an additional switch (not shown), when the current source 204 isactive (i.e. when the control switch 203 is closed). As such, theinternal resistor 223 can be made infinitive, when measuringfree-wheeling. Additionally, the resistor R3 223 can be provided withseveral values for adjusting a larger range for the resistors R1 201 andR2 202 and the charge current.

A further option may be to replace the resistor R3 223 by a currentmirror as illustrated in FIG. 2 d. FIG. 2 d shows an excerpt of afurther example power converter using a single sensing pin 130 forcharging the supply voltage capacitor, for measuring the input voltageand for measuring free-wheeling. In FIG. 2 d the current source 204 andthe control switch 203 are not shown, but may be provided for measuringfree-wheeling at the comparator 205. A Zener diode 246 may be used toprotect the input of the comparator 205.

In FIG. 2 d, the resistor R3 223 is replaced by an additional currentsource 243 and a current mirror formed by the transistors 242 and 244.Furthermore, an additional switch 241 may be used to couple the currentmirror and the current source to the sensing pin 130, when measuring theinput voltage, and to decouple the current mirror and the current sourcefrom the sensing pin 130, when measuring free-wheeling. The use of acurrent mirror and current source is beneficial in order to clamp thevoltage drop at the additional comparator 245 to a certain (relativelylow) level. The measurement of the input voltage may be performed usingthe additional comparator 245 arranged at one side of the currentmirror. The current mirror can be switched off using the switch 241. Themirror and/or the current source can be adjusted. It should be notedthat instead of the current source 243, a resistor may be used and thevoltage at the resistor can be measured. The current mirror may beimplemented as a cascaded current mirror to improve the linearity of thecurrent mirror. It should be noted that there are other possibilitiesfor implementing the function of the current mirror (e.g. an activecurrent mirror comprising an operational amplifier).

FIG. 3 illustrates an example method 300 which makes use of a mainsswitch 301 as signaling means, in order to encode a plurality of events310. The example events of FIG. 3 are an “ON” event, corresponding to aswitch 301 which is kept on for a minimum pre-determined time interval;an “OFF event, corresponding to a switch 301 which is kept off for aminimum pre-determined time interval; and an “OFF/ON” event,corresponding to an event where the switch 301 is briefly switched fromON to OFF and then back to ON within a predetermined time interval.These three events in combination with various illumination states canbe used to provide a dimming function (even when no phase-cut dimmer isavailable at the mains supply). The three events may be detected by thecontroller 160 via the startup and input voltage sensing pin 130. By wayof example, the controller 160 may be configured to determine whetherthe input voltage (e.g. the root means squared value of the inputvoltage) is greater than or smaller than a voltage threshold, therebydetermining whether the mains switch 301 is switched on or off.

It can be seen from FIG. 3, how the ON event 312 can be used to changethe driver circuit 100 from the state “OFF”, i.e. no intensity,(reference numeral 322) to the state “MAX”, i.e. maximum intensity,(reference numeral 321), and how the OFF event 311 can be used toperform the inverse change of states. When in the “MAX” state 321, theOFF/ON event 313 can be used to put the driver circuit 100 into a dimdown state 323. The dim down state 323 triggers a smooth decrease inintensity down towards a minimum intensity (e.g. 20% intensity). Usinganother OFF/ON event 314, the dim down state 323 may be stopped, therebyputting the driver circuit 100 into a hold state 324 at the currentintensity. When detecting another OFF/ON event 316, the driver circuit100 is put into a dim up state 325, thereby smoothly increasing theintensity up to the maximum intensity. Another OFF/ON event 317 mayagain put the driver circuit 100 into a hold state 326 (which differsfrom the hold state 324 in that a subsequent OFF/ON event 318 willretrigger the dim down state 323, instead of the dim up state 325).Whenever detecting an OFF event 315, 519, the driver circuit 100 is putinto the OFF state 322. In the example method 300 (and the correspondingexample state machine of the controller 206), this OFF state 322 canonly be left, when detecting an ON event 312.

As such, the driver circuit 100 of FIGS. 2 a and 2 b may be configuredto measure the input voltage of the SEPIC (i.e. to measure the mainsvoltage) and to measure free-wheeling of the SEPIC transformer 162 usinga single sensing pin 130. The measured input voltage may be used tocontrol the illumination state of the LED array 120 (using e.g. themethod 300) and the detected time instant of free-wheeling may be usedto control the switching time instant of the SEPIC power converter 163.As a result of using only a single sensing pin 130, the cost of thedriver circuit 100 (and the cost of the light bulb assembly 1 comprisingthe driver circuit 100) can be reduced.

FIG. 4 illustrates the flow chart of an example method 400 forconverting electrical energy at an input voltage into electrical energyat an output voltage using a power converter 191, 192. Step 401 of thedisclosed method depicts providing a controller comprising a singlesensing pin, controlling a power converter comprising a power switch.Step 402 describes switching a power switch 163, 173 of the powerconverter 191, 192 between an on-state and an off-state, subject to acontrol signal. Furthermore, step 403 teaches providing a firstmeasurement signal from the power converter 191, 192 to the controller160 via a sensing pin 130, 140 of the controller 160, when the powerswitch 163, 173 is in on-state. The first measurement signal may beindicative of a voltage or a current at a particular node within thepower converter. Examples of the first measurement signal are e.g. theinput voltage of the power converter and/or a current through the powerswitch. Step 404 further describes providing a second measurement signalfrom the power converter 191, 192 to the controller 160 via the samesensing pin 130, 140 of the controller 160, when the power switch 163,173 is in off-state. The second measurement signal may be indicative ofa voltage or a current at a particular node within the power converter.Examples of the second measurement signal are the input voltage of thepower converter and/or the voltage drop at a transformer or awinding/coil of the power converter. Step 405 illustrates generating thecontrol signal for putting the power switch 163, 173 into the on-stateand into the off-state, respectively, based on the first and/or thesecond measurement signal. In particular, the current through the powerswitch may be used as a trigger to switch off the power switch (e.g.when reaching a pre-determined peak current). Alternatively or inaddition, the voltage drop at the transformer may be used as a triggerto switch on the power switch (e.g. when detecting free-wheeling of thetransformer).

It should be noted that the description and drawings merely illustratethe principles of the proposed methods and systems. Those skilled in theart will be able to implement various arrangements that, although notexplicitly described or shown herein, embody the principles of theinvention and are included within its spirit and scope. Furthermore, allexamples and embodiment outlined in the present document are principallyintended expressly to be only for explanatory purposes to help thereader in understanding the principles of the proposed methods andsystems. Furthermore, all statements herein providing principles,aspects, and embodiments of the invention, as well as specific examplesthereof, are intended to encompass equivalents thereof.

The invention claimed is:
 1. A power converter configured to convertelectrical energy at an input voltage into electrical energy at anoutput voltage, the power converter comprising a power switch configuredto be switched between an on-state and an off-state; a voltage dividercoupled to the input voltage for providing a first measurement signal; atransformer comprising a primary winding and an auxiliary winding forproviding a second measurement signal; wherein the primary winding isarranged in series to the power switch; and a controller configured togenerate a control signal for putting the power switch into the on-stateand into the off-state, respectively; wherein the control signal isgenerated based on the first and the second measurement signal from thepower converter external to the controller; wherein the controllercomprises a sensing pin configured to sense the first measurement signalwhen the power switch is in the on-state, and configured to sense thesecond measurement signal when the power switch is in the off-state,wherein the auxiliary winding is coupled to the sensing pin, therebyproviding the second measurement signal; the auxiliary winding iscoupled to the sensing pin via a diode; and the diode is reverse biased,when the power switch is in on-state, thereby decoupling the auxiliarywinding from the sensing pin, when the power switch is in on-state. 2.The power converter of claim 1, wherein the voltage divider comprises ahigh side resistor; and wherein the high side resistor is coupled to thesensing pin, thereby providing the first measurement signal.
 3. Thepower converter of claim 1, wherein the controller comprises a currentsource which is coupled to the sensing pin via a control switch andwhich is coupled to ground; and the control switch is opened, when thepower switch is put to the on-state, and is closed when the power switchis put to the off-state.
 4. The power converter of claim 1, wherein thecontroller comprises a comparator configured to measure a voltage at thesensing pin.
 5. The power converter of claim 1, wherein the controlleris configured to operate the power converter according to a currentoperation state; detect one of a plurality of pre-determined eventsbased on the first and/or the second measurement signal; determine atarget operation state in accordance with a pre-determined statemachine, based on the current operation state and based on the detectedone of the plurality of pre-determined events; and operate the powerconverter in accordance with the target operation state.
 6. The powerconverter of claim 2, wherein the power converter comprises a supplyvoltage capacitor coupled to a supply voltage pin of the controller; andthe controller is configured to couple the sensing pin to the supplyvoltage pin upon startup of the power converter to charge the supplyvoltage capacitor via the high side resistor of the voltage divider. 7.The power converter of claim 4, wherein the controller comprises astartup diode which is configured to let pass a current from the sensingpin to the supply voltage pin, and which is configured to block acurrent from the supply voltage pin to the sensing pin.
 8. The powerconverter of claim 5, wherein the controller comprises a startup switchconfigured to decouple a measurement circuitry for measuring the firstand second measurement signals, when the startup switch is open.
 9. Thepower converter of claim 2, wherein the voltage divider comprises a lowside resistor coupled to ground; and a midpoint of the voltage dividerbetween the high side resistor and the low side resistor is coupled tothe sensing pin, thereby providing the first measurement signal.
 10. Thepower converter of claim 2, wherein the voltage divider comprises acurrent mirror arranged in series with a second current source; thecurrent mirror and the second current source are internal to thecontroller; a first side of the current mirror is coupled to the sensingpin and a second side of the current mirror is coupled to the secondcurrent source; and the controller comprises a second comparatorconfigured to measure the first measurement signal at the second side ofthe current mirror.
 11. A light bulb assembly comprising an electricalconnection module configured to electrically connect to a mains powersupply, thereby providing electrical energy at the input voltage; apower converter, configured to provide electrical energy at an outputvoltage from the electrical energy at the input voltage, the powerconverter comprising: a power switch configured to be switched betweenan on-state and an off-state; a voltage divider coupled to the inputvoltage for providing a first measurement signal; a transformercomprising a primary winding and an auxiliary winding for providing asecond measurement signal; wherein the primary winding is arranged inseries to the power switch; and a controller configured to generate acontrol signal for putting the power switch into the on-state and intothe off-state, respectively; wherein the control signal is generatedbased on the first and the second measurement signal from the powerconverter external to the controller; wherein the controller comprises asensing pin configured to sense the first measurement signal, when thepower switch is in the on-state, and configured to sense the secondmeasurement signal, when the power switch is in the off-state, whereinthe auxiliary winding is coupled to the sensing pin, thereby providingthe second measurement signal; the auxiliary winding is coupled to thesensing pin via a diode; and the diode is reverse biased, when the powerswitch is in on-state, thereby decoupling the auxiliary winding from thesensing pin, when the power switch is in on-state; and a light sourceconfigured to provide light using the electrical energy at the outputvoltage.
 12. The light bulb assembly of claim 11, wherein the lightsource comprise a solid state lighting device.
 13. A method forconverting electrical energy at an input voltage into electrical energyat an output voltage, the method comprising providing a controllercomprising a sensing pin, controlling a power converter comprising apower switch; switching a power switch of a power converter between anon-state and an off-state, subject to a control signal; providing afirst measurement signal from the power converter to a controller viathe sensing pin of the controller, when the power switch is in theon-state; wherein the first measurement signal is derived from a voltagedivider coupled to the input voltage; providing a second measurementsignal from the power converter to the controller via the sensing pin ofthe controller, when the power switch is in the off-state; wherein thesecond measurement signal is derived from a transformer comprising aprimary winding arranged in series with the power switch; and generatingthe control signal for putting the power switch into the on-state andinto the off-state, respectively, based on the first and/or the secondmeasurement signal, wherein the transformer comprises an auxiliarywinding which is used for measurement purposes; and it is ensured thatthe provision of the first measurement signal is not disturbed by thesecond measurement signal by coupling the sensing pin via a diode to theauxiliary winding, wherein the diode is reverse biased in order todecouple the auxiliary winding from the sensing pin, when the powerswitch is in the on-state.
 14. The method of claim 13 wherein the powerconverter is used in a driver circuit for a light bulb assembly, whereinoperation states of the power converter correspond to differentillumination states of the light bulb assembly.
 15. The method of claim13 wherein the control signal is a pulse-width modulated signal.
 16. Themethod of claim 13 wherein the first measurement signal is indicative ofan input voltage of the power converter and/or a current through thepower switch.
 17. The method of claim 13 wherein the second measurementsignal is indicative of an input voltage of the power converter and/or avoltage drop at a transformer or at a winding/coil of the powerconverter.
 18. The method of claim 13 wherein the controller is providedwith a plurality of different measurement signals using only the sensingpin.
 19. The method of claim 18 wherein the sensing pin is configured tosense the first measurement signal, when the power switch is in theon-state, and configured to sense the second measurement signal, whenthe power switch is in the off-state.
 20. The method of claim 18 whereininformation regarding the input voltage comprises information used forcontrolling the operational state of the power converter.
 21. The methodof claim 18 wherein the sensing pin of the controller is used to providethe controller with information regarding an input voltage and withinformation regarding a zero crossing of an inductor current through aprimary winding of the transformer, when the power switch is inoff-state wherein the zero crossing of the inductor current correspondsto a time instant when no more energy is stored in the primary windingof the transformer and is referred to as free-wheeling of thetransformer.
 22. The method of claim 21 wherein the informationregarding the free-wheeling of the transformer of the power convertercomprises information used for determining the time instant for puttingthe power switch to on-state.
 23. The method of claim 22 wherein theauxiliary winding is used to detect the free-wheeling state of thetransformer.
 24. The method of claim 13 wherein the method steps areperformed by a software program, which is adapted for execution on aprocessor.